While skins have great variety as far as possible gameplay differences, there are still limitations. Castlevania and Ninja Gaiden offer differences with each installment, so the only way to convey this would be making Simon and Trevor separate characters and adding Ken Hayabusa as well. Here's how it would work... Simon would have Vampire Killer styled gameplay. Only Holy Water and Stopwatch uses hearts. The Knife/Boomerang/Axe replaces whip when obtained. There are only two Knifes on screen at a time. Then the Boomerang travels full screen, the Axe doesn't arch, but travels like Boomerang just only half screen and is stronger. If the Boomerang or Axe isn't caught, Simon loses it and goes back to default whip. Additional powerups such as Boots for faster running speed, and Wings for higher jump height could also be added. Meanwhile, Trevor retains the classic Castlevania gameplay. Ryu would be based on Ninja Gaiden 3. He has the Sword Extension, but not the Jump Slash. Ken is based on the first Ninja Gaiden. He has the Jump Slash, but not the Sword Extension. Ken can only cling to walls, and not climb them. To compensate he would be able to double jump.